Does there has any easy way to convert "02:00" to minutes say 120?

Question

Does there has any easy way to convert "02:00" to minutes say 120 ?

Do we have to split it to 2 and then * 60 ?

Check this out: https://stackoverflow.com/questions/11213326/how-to-convert-a-string-variable-containing-time-to-time-t-type-in-c — Nanev, Sep 12 '18 at 14:36
@YSC I'm unsure about the dupe. There is no need at all to convert the string into a `time_t` to just have to do more math to convert it's hours and minutes into total minutes. We can do that directly from the sting like `((time[0] - '0') * 600) + ((time[1] - '0') * 60) + ((time[3] - '0') * 10) + (time[4] - '0')` — NathanOliver, Sep 12 '18 at 14:48
That's true, it might answer OP's question, but it is no certainty. — YSC, Sep 12 '18 at 14:51

Howard Hinnant · Answer 1 · 2018-09-13T14:10:55.690

Here's how to do it using Howard Hinnant's date/time library:

#include "date/date.h"
#include <cassert>
#include <iostream>
#include <sstream>

int
main()
{
    using namespace date;
    using namespace std;
    using namespace std::chrono;
    istringstream in{"02:00"};
    minutes m;
    in >> parse("%H:%M", m);
    assert(m == 120min);
}

Additionally this should port to the upcoming C++20 spec by simply removing #include "date/date.h" and using namespace date;.

The advantage of this technique includes:

No need to manually split the string
No need for manual conversion from hours to minutes
The result goes straight into the chrono type safe units
No need to dip down to the old C API

score 1 · Accepted Answer · answered Sep 12 '18 at 15:00

You don't need to split anything here. In "12:34" the 1 represents the tens of hours, the 2 is how many single hours, the 3 is the tens of minutes and the 4 is the single minutes. Knowing that you can multiply each position by how many minutes it represents.

If we have

std::sting time = "12:34"

then (time[0] - '0') * 600 would give use 600 minutes (time[0] - '0' converts the character '1' to the number 1). (time[1] - '0') * 60 would be 120 more minutes. If we keep going we'd have

((time[0] - '0') * 600) + ((time[1] - '0') * 60) + ((time[3] - '0') * 10) + (time[4] - '0')

And all of that added up gives use 754 minutes. You can put that into a function if you have to do it multiple times.

score 1 · Answer 3 · answered Sep 12 '18 at 15:21

Maybe you like this one:

std::tm tm = {}; 
std::stringstream ss("20:05");
ss >> std::get_time(&tm, "%H:%M");
std::cout << tm.tm_hour * 60 + tm.tm_min << std::endl;

Maybe it is much to much overhead using this big library calls in your case, but maybe you have to deal with more complex time strings.

Does there has any easy way to convert "02:00" to minutes say 120?

3 Answers3